Add UMA metrics to the site engagement service.

chrome/browser/engagement/site_engagement_metrics.h

Index: chrome/browser/engagement/site_engagement_metrics.h
diff --git a/chrome/browser/engagement/site_engagement_metrics.h b/chrome/browser/engagement/site_engagement_metrics.h
new file mode 100644
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+++ b/chrome/browser/engagement/site_engagement_metrics.h
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+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_METRICS_H_
+#define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_METRICS_H_
+
+#include <map>
+
+#include "url/gurl.h"
+
+// Helper class managing the UMA histograms for the Site Engagement Service.
+class SiteEngagementMetrics {
+ public:
+  // This is used to back a UMA histogram, so it should be treated as
+  // append-only.
+  enum EngagementType {
+    ENGAGEMENT_NAVIGATION,
+    ENGAGEMENT_KEYPRESS,
+    ENGAGEMENT_MOUSE,
+  };
+
+  static void RecordTotalCumulativeSiteEngagement(double total_engagement);
+
+  static void RecordTotalOriginsEngaged(int total_origins);
+
+  static void RecordEngagementPerOrigin(std::map<GURL, double> score_map);
+
+  static void RecordOriginsWithMaxEngagement(int total_origins);
+
+  static void RecordOriginsWithMaxDailyEngagement(int total_origins);
+
+  static void RecordEngagement(EngagementType type);
+
+};
+
+#endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_METRICS_H_